The present invention is directed to an electrical switching apparatus particularly suited for door actuated operation and configured to facilitate conversion for grounded or non-grounded operation.
Numerous devices have long been available for door actuated operation, such as the devices disclosed and U.S. Pat. Nos. 2,921,155; 3,393,281; and 3,432,634 all by M. J. Basso; as well as 3,244,829 by G. L. Webb and 3,251,971 by R. W. Fraser.
For example, a device disclosed by Webb in U.S. Pat. No. 3,244,829 has become nearly an industry standard in many applications of door actuated devices associated with automotive applications, such as lighting circuits. The Webb device is a grounded operating switch, meaning that the supply of power to the lighting device is connected to ground through the switch to complete the circuit and effect illumination of the light bulb.
The Basso devices disclosed in the patents cited above provide a variety of door actuated switches particularly associated with the automotive industry. Basso's U.S. Pat. No. 3,393,281 provides a door actuated push-button switch which is usable for grounded or non-grounded applications. Proper selection of the particular terminals associated with that switch determine whether grounded or non-grounded operation is effected. Basso's U.S. Pat. Nos. 3,432,634 and 2,921,155 disclose self-adjusting features for switches of a door closure switch. Fraser's U.S. Pat. No. 3,251,971 likewise illustrates a self-adjusting feature for a door actuated switch.
There are two particular shortcomings of the prior art switches which are hereinabove discussed which are overcome by the present invention.
First, there is a need for a switch which can be, during its manufacture, easily established to be a grounded or a non-grounded operating switch. Such factory-determination of the mode of operation of the switch precludes confusion in installation of the switch in the field which could damage the electrical circuitry by connecting incorrect connectors for the particular mode of operation desired. Further, by having an easily converted switch, as is provided by the present invention, fewer special parts are needed to effect the determination of mode of operation of the switch, thus yielding greater economy and flexibility in its manufacture to accommodate the two basic types of switching operations encountered in field applications.
Second, a common problem among all of the prior art switches, especially in automotive applications, is the ingress of contaminants (particularly water) to the interior of the switch. Ingress of water to the interior of the switch in the area of the contacts of the switch frequently establishes a leakage path through the water contaminant from the movable contacts to the fixed contacts when the door is closed and the switch is in its open position. Such a leakage path produces at least two problems: (1) an electrical path is established where no such path is desired, resulting in possible inadvertent operation of the equipment controlled by the switch and depletion of the power source, generally a battery in automotive applications; and (2) a low level leakage current through the contaminant establishes conditions ripe for an ionizing process which can produce oxides on the respective terminals, thereby decreasing their effectiveness as electrical conductors with consequent decreases in effectiveness of the switching operations during subsequent actuations of the switch.